[release/7.0-rc1] [wasm] Reduce allocation when options are passed to fetch

[github-actions]

Backport of #74142 to release/7.0-rc1

/cc @maraf

Customer Impact

Reduce allocation of List<T> when passing options to fetch.

Testing

Unit tests.

Risk

None.

IMPORTANT: Is this backport for a servicing release? If so and this change touches code that ships in a NuGet package, please make certain that you have added any necessary package authoring and gotten it explicitly reviewed.

[ghost]

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Backport of #74142 to release/7.0-rc1

/cc @maraf

Customer Impact

Testing

Risk

IMPORTANT: Is this backport for a servicing release? If so and this change touches code that ships in a NuGet package, please make certain that you have added any necessary package authoring and gotten it explicitly reviewed.

Author:	github-actions[bot]
Assignees:	-
Labels:	area-System.Net.Http
Milestone:	-

[ghost]

Tagging subscribers to 'arch-wasm': @lewing
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Backport of #74142 to release/7.0-rc1

/cc @maraf

Customer Impact

Reduce allocation of List<T> when passing options to fetch.

Testing

Unit tests.

Risk

None.

IMPORTANT: Is this backport for a servicing release? If so and this change touches code that ships in a NuGet package, please make certain that you have added any necessary package authoring and gotten it explicitly reviewed.

Author:	github-actions[bot]
Assignees:	-
Labels:	arch-wasm, area-System.Net.Http
Milestone:	-

[carlossanlop]

@marek-safar@lewing@pavelsavara need an area owner sign off and someone to approve the backport.

[carlossanlop]

Approved, signed-off and CI passed. Ready to merge.